The ornamental design for a handle for a handheldtool, as shown and described.
FIG. 1 is a front perspective view of a handle for a handheld tool showing my new design;
FIG. 2 is a front side elevational view thereof, the rear side elevational view and the left and right side elevational views being the same as FIG. 2;
FIG. 3 is a top plan view thereof; and,
FIG. 4 is a bottom plan view thereof.
The broken lines in the figures show an example environment and form no part of the claimed design.